A wide variety of implantable medical devices (IMDs) have been developed in order to monitor patient conditions and deliver therapy to the patient. An IMD typically includes a hermetically sealed housing coupled to one or more leads that are surgically implanted inside a patient for short or long term therapy. The IMD may provide therapeutic stimulation to the patient or may deliver drugs or agents to the patient. Alternatively or additionally, the IMD may have sensing or monitoring capabilities. For example, the IMD may sense information within a patient and store the sensed information for subsequent analysis. Telemetry can be used to communicate sensed information from the IMD to an external medical device so that analysis can be performed. Also, in some cases, the sensed information may be used directly by the IMD to adjust or control the therapy that is delivered to the patent.
One common example of an IMD is a pacemaker. A pacemaker typically includes a pacemaker device and one or more pacing and sensing leads for delivery of pacing pulses to a patient's heart and sensing of heart conditions. Another example of an IMD is a combination pacemaker-cardioverter-defibrillator. Other examples include implantable brain stimulators, implantable gastric system stimulators, implantable nerve stimulators or muscle stimulators, implantable lower colon stimulators, implantable drug or beneficial agent dispensers or pumps, implantable cardiac signal loops or other types of recorders or monitors, implantable gene therapy delivery devices, implantable incontinence prevention or monitoring devices, implantable insulin pumps or monitoring devices, and so on.
IMDs often sense and record electrograms or other biomedical information associated with a patient. Electrograms refer to signals which represent recorded changes in electric potential of the patient. Examples of electrograms include electrocardiograms, i.e., recorded electrical potentials associated with a patient's heart, and electroencephalograms, i.e., recorded electrical potentials associated with a patient's brain. Other more specific examples of electrograms include atrial electrograms, coronary sinus (CS) electrograms, esophageal electrograms, high right atrial (HRA) electrograms, His bundle electrograms, intra-atrial electrograms, intracardiac electrograms, left and right ventricular electrograms, right ventricular apical electrograms, sinus node electrograms, and the like.
IMDs typically sense and store information in a continuous fashion. In many cases, the stored information is averaged over whole or half days. For example, measurements of a patient's heart rate may be continuously measured and averaged. Similarly, measurements of amplitudes or frequency associated with specific features of electrocardiograms may be accumulated in a continuous fashion. However, continuous monitoring techniques can limit the diagnostic usefulness of the measured information.